A single application may use multiple Logical Units (LUs). For example, a database system may have a log file on one LU and a data file on another LU. Databases may employ a backup technique which takes a snapshot of database LUs, and backup the snapshots to an appropriate storage media, such as tape. Such a backup technique may be performed without offlining the database; the database may not quiesce I/O (input/output) functionality. For instance, the database application may continue to run while snapshots are taken, where the snapshots may not be coordinated with the database activity. The snapshot backup technique may require a consistent snapshot of all LUs used by the database application before a backup may be performed. This consistency may ensure that the application actually be restored correctly from the backup.
A consistency group (CG) may be used when database systems have LUs located on different storage arrays. A CG may consist of one or more LUs, and may be used to create a snapshot of all members of the CG as a single atomic operation.